The invention relates to a take-out roll, spreader roll, or equivalent for a web-like material, which roll comprises three parts linked with one another, i.e. two end parts and a middle part, which parts are pivotal with respect to one another for the purpose of bending the roll into a desired curved shape.
Take-out rolls and spreader rolls have been formed most commonly so that they have a continuous axle and a roll mantle fitted on the axle, which roll mantle is in turn composed of a number of parts. The take-out roll can be made to be curved into a desired shape by shifting the outer journalling points of the roll mantle in the radial direction, whereby the mantle forms an arc or a broken line. Each of the mantle parts is generally journalled separately on the axle, in which case the arrangement comprises a number of bearings. The conventional arrangements involve a number of problems and drawbacks, which are, among other things, problems of journalling of the roll and peaks of heat produced by the journalling in the paper web. The making of the mantle of several parts may also constitute a considerable problem because the gaps between the parts may mark the paper web and because the arc form of the roll is not optimal, but the line of shape of the roll is shaped as a broken line. Further, owing to the metallic roll mantle, problems of corrosion may arise. One such prior-art spreader roll is described, for example, in the U.S. Pat. No. 4,692,971. Attempts have been made to provide an improvement over such a prior-art spreader roll, for example, so that a coating layer of a resilient material has been fitted onto the metal mantle consisting of a number of parts, the objective of this arrangement being in particular to provide an improvement concerning the problem of marking of the paper web and concerning optimization of the arc form of the roll. However, the journalling system of the roll is similar to that described above, and, thus, also the problems related to the journalling are unchanged. Such a spreader roll is described, for example, in the Canadian Patent No. 766,843.
Previously, attempts have been made to find a solution to the problem arising from a roll mantle made up of several parts also so that, as the roll mantle, a continuous metal tube mantle has been used which has been provided with xe2x80x9ccutsxe2x80x9d, i.e. into which slots have been formed in order to facilitate the bending of the roll mantle. This construction, however, causes its own problems, one worth noticing being the fact that, owing to its construction, the roll mantle becomes quite slack, i.e. excessively readily bending. In such a case, the roll mantle concerned must be supported on the roll axle by means of bearings at a number of points, for which reason the problems described above and arising from the journalling remain unchanged. Also, the cost of manufacture of the roll mantle is relatively high because of the mode of manufacture.
The greatest problems of present take-out rolls, spreader rolls and equivalent are mainly due to the construction of the roll in use, which is most commonly a construction of the kind in which the roll comprises a non-revolving roll axle and a roll mantle revolvingly journalled on it. In addition to the prior art publications already cited previously, reference is made in this connection to the Finnish Patent Application No. 951921, which fairly representatively describes the prevailing prior art. More specifically, said publication describes a roll comprising a continuous and non-revolving roll axle. A roll mantle made up of three parts, i.e. a middle part and end parts, is fitted on the axle. The middle part is journalled in the area of its both ends directly on the axle of the roll. The inner ends of the end parts are also journalled directly on the axle and the outer ends are similarly journalled on separate sleeve parts, whose inside diameter is larger than the diameter of the axle. The sleeve parts can be shifted radially, whereby the roll mantle curves or, more exactly, attains the shape of a broken line, when the outer ends of the end parts of the mantle move radially with respect to the inner ends. The roll is thus provided with a desired xe2x80x9ccurvedxe2x80x9d shape.
However, all the arrangements of today involve the drawback that there are journalling points in the inner area of the roll mantle, that is, in the area of the web. Firstly, arrangement of lubrication of these bearings is at least principally difficult to provide. A second, even more serious drawback is that the bearings heat up during operation with the result that this heating up produces a thermal gradient in paper. Heat is transferred with the paper into a roll nip and, at worst, it may cause burning of a soft nip roll. In the FI Application 951921, for example, attempts have been made to solve this problem in such a way that thermal insulation material is provided in connection with the bearings situated in the area of the web for the purpose of reducing the transfer of heat from the bearings to the paper web. The structure of the roll has, however, become very complicated and expensive, and yet it has not been possible to eliminate all drawbacks.
The object of the present invention is to provide a novel construction of a take-out roll, spreader roll, or equivalent, by means of which the problems related to the prior art described above are avoided. With a view to achieving the objective of the invention, the invention is mainly characterized in that the middle part of the roll is constructed to also operate as a revolving axle of the roll, which is mounted revolvingly on its support members by means of end bearings, and that the end parts of the roll are mounted, in the area of their axial inner ends, on the middle part by means of articulation devices.
The invention provides quite a considerable advantage over the prior art, and of the advantages obtainable by means of the invention, for example, the following may be mentioned. The roll does not comprise across the width of the web any lubrication points that impede the use of the roll and make its use more difficult. Also, there has been no need to place any bearings in the roll in the area of the width of the web, thereby making it possible to avoid the problems of the prior art caused by heating up of bearings. Considerably smaller bearings may be used in the roll as compared with conventional take-out rolls, bearing frictions being then also smaller than previously. The number of bearings has been made smaller than previously, since the roll needs only four roller bearings, whereas the rolls in accordance with the prior art usually comprised at least six roller bearings and two glide bearings. The axle of the roll is substantially more rigid than in the previous arrangements, which employ a separate non-revolving axle. A possible drive is very easy to arrange by coupling a drive means simply to the end of the roll axle. Owing to the construction in accordance with the invention, for example, a composite material may be used as the roll material. In that case, the roll is advantageously constructed as a shell structure, whereby the roll becomes fairly light in weight and its lowest specific frequencies can be raised so high that the support provided by the end journalling of the roll is sufficient for support of the entire roll. The further advantages and characteristic features of the invention come out from the following detailed description of the invention.